1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a turbine rotor blade with a serpentine flow cooling circuit.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
A turbine rotor blade is cooled using a serpentine flow cooling circuit in which cooling air flows upward to the blade tip region and then turns 180 degrees and flows toward the platform region in order to extend the length of the cooling air path and provide increased cooling effectiveness. FIG. 1 shows a 5-pass aft flowing serpentine blade cooling design with a first leg 11 located adjacent to a leading edge region cooling circuit and the remaining four legs extending toward the trailing edge region. The first leg 11 turns into the second leg 12 at the blade tip region to also provide impingement cooling to an underside of the blade tip. The third leg 13 also turns into the fourth leg at the blade tip region. The first leg 11 supplies a showerhead arrangement of film cooling holes and gill holes to provide cooling to this region. The fifth leg 15 of the 5-pass serpentine flow circuit provide cooling air for a trailing edge region cooling circuit that includes double impingement followed by discharge through exit slots arranged along the trailing edge of the blade. FIG. 2 shows a cross section view of the 5-pass serpentine flow cooling circuit and FIG. 3 shows a flow diagram of the 5-pass serpentine flow cooling circuit of FIG. 1.
FIG. 1 also shows two core print-out holes 17 at the two turns of the 5-pass serpentine flow cooling circuit that function as dirt holes that purge particulates such as small dirt particles from the cooling air using centrifugal force. Any dirt particulates within the cooling air flow will fall out of the turn by passing straight through the dirt hole 17 instead of making the 180 degree turn into the next down flow channel of the serpentine circuit. Any dirt particulates that are not discharged from the first dirt hole 17 will theoretically pass out from the second dirt holes at the end of the third leg 13. Use of the dirt holes 17 in the serpentine flow circuit will discharge some of the cooling air from the blade. The size of the dirt holes depends upon the size of the blade. for a large frame heavy duty industrial gas turbine (IGT) engine, the dirt hole size can be in a range of 2-4 mm. this size dirt holes results in 0.1% to 0.2% of the total engine flow being discharged through each of the dirt holes 17.